(a) Field of the Invention
The present invention relates to a shift control method of an automatic transmission. More particularly, the present invention relates to a shift control method of an automatic transmission that controls a shift from an nth shift speed to an (n−3)th shift speed.
(b) Description of the Related Art
Generally, in a clutch-to-clutch shift control, one frictional element is released and another frictional element is engaged. However, during some skip shifting processes, two frictional elements may be released and two other frictional elements may be engaged. However, it is difficult to control such a shift.
In some instances, two shifting processes are successively performed. For example, to perform a 6 to 3 shift, a 4 to 3 shift is performed after a 6 to 4 shift is completed.
However, according to a conventional 6 to 3 skip shift control method, since two shifting processes are successively performed, a shifting time may be long, and the shift may not be smooth.
To solve such problems, the first and second shifts may be overlapped. However, a double shift feel may be felt. In addition, since controls of on-coming and off-going elements in the second shift are started differently, shift control may be difficult, since a shift to another shift speed is needed during the 6 to 3 shift.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.